We provide broadband dielectric spectra on aqueous lysozyme solutions of
various concentrations and analyze the three dispersion regions commonly
found. The beta-dispersion, occurring in the frequency range around 10 MHz
and the gamma-dispersion arising around 20 GHz can be attributed to the
rotation of the polar protein molecules in the aqueous medium and the
reorientational motion of the free water molecules, respectively. The nature
of the third relaxation (delta-relaxation) around 100 MHz, which is often
ascribed to the motion of protein-bound water molecules, is not yet fully
understood and the hydration-shell dynamics of biomolecules is an ongoing
field of research [1-3]. Additional insight can be gained by analyzing the
subzero temperature spectra, where the beta- and gamma-dispersions, which
partly superimpose the delta-relaxation for temperatures above 273 K,
disappear due to the freezing of the bulk water. In contrast, the water
molecules in the protein hydration shell are known to remain in the liquid
state well below the freezing point. This allows to investigate the
delta-relaxation in an extended temperature range and to shed new light on
the hydration-shell dynamics of biomolecules.\\[4pt]
[1] W. Doster, S. Cusack, and W. Petry, Nature \textbf{337}, 754 (1989).\\[0pt]
[2] M. Vogel, Phys. Rev. Lett. \textbf{101}, 225701 (2008).\\[0pt]
[3] A. Benedetto, Biophys. Chem. \textbf{182}, 16 (2013).

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.MAR.Y11.7